1. Technical Field
The present invention relates to a respiratory heat and moisture exchanger, heat and moisture exchanging device, and mask, and more particularly, to a respiratory heat and moisture exchanger, heat and moisture exchanging device, and mask for appropriately adjusting the temperature and moisture of a gas such as air for a patient to inhale.
2. Related Art
Two kinds of devices have been usually employed to humidify and warm an aspired (inhaled) dry gas when using an anesthesia device, a respirator, or other devices.
One is a heat and moisture exchanging device (HME, called an “artificial nose”) of a passive type, and the other is a warmer/humidifier of an active type operated with a heat source.
The passive HMEs are further categorized into three types:                a type having hydrophilic material charged with hydroscopic substance;        a type having hydrophobic material charged with hygroscopic substance; and        a type having a combination of hydrophobic and hydrophilic layers.        
For example, Japanese Patent Application Laid-open Publication No. H06-63141 discloses the third type HME. In the reference, entitled “Heat and Moisture Exchanger (Filter)—Element Device and Humidification—”, Japanese Journal of Respiratory Care Medicine 21-1, P. 1-7, edited by K. Ishii, described in detail are the HMEs.
For all types, it is understood that some amount of water vapor in the expiratory (exhaled) gas is condensed at a dew point in spaces minutely formed in an element of the HMEs, and meanwhile, the aspiratory gas serves to evaporate the condensed water for humidification. In case of warming of aspiratory gas, it is predicted that there will occur cyclic and local phenomena of thermal storage or heat storage.
At present, the passive types are prevailing because of the advantages of being compact, lightweight, and low-cost while minimizing the risk of medical accidents, mainly arising from usage of a heat source and lack of humidifying due to failure in supplying additional water in the active type. However, it is a fact that as far as performance in warming and humidifying is concerned, the passive types are generally inferior when compared to the active ones.
The above conventional HMEs, however, have the following problems. One problem is that an airway of a patient tends to dry because of poor warming and humidifying capability and a fatal complication may be resulted by suffocation of the airway due to hardening of secretions. Another problem is clogging caused by condensed water accumulated in the HME.
In order to solve the above problems, it is required to store larger amount of water in an expiratory gas and release the stored water into an aspiratory gas. The amount of water to be stored in the HME is preferably 44 mg/l, a saturated vapor amount in the air of 37° C. of a normal body temperature. It is very important that in aspiration (inhalation), the aspired gas is required to be near at the patient body temperature, as well as to keep high recovery of the absolute humidity. In storing and releasing of the above-mentioned amount of water, the thermal storage capability of the HMEs has to be improved for maintaining the required temperature.
In order to achieve the same purpose, HMEs with a thermal storage unit made of metal or the like, have been proposed. However, those metal type HMEs have several problems such as its bulkiness and heavy weight, and necessity of cleaning every time secretions stick thereto. Thus, the disposable HMEs, being small, light-weight, and inexpensive, have become in use.
On the other hand, it is not always preferable that the higher thermal storing effect is equipped with HMEs. For example, in the case that a humid expiratory gas of 37° C. enters into an anesthesia circuit via an HME from a patient in an operating room, condensation in the circuit is likely to occur because of large difference in temperature between the expiratory gas and typical room environment (23° C.).
Furthermore, if a dead cavity and/or a flow resistance are increased, there may occur a risk of increased burden on the patient required for breathing.
When anesthesia or artificial respiration is applied, the patient requires the aspiratory gas of 44 mg/l in absolute humidity, corresponding to relative humidity of 100% at a body temperature of 37° C. It is desired that the temperature of the aspiratory gas is adjusted closer to a body temperature for the required absolute humidity. If the temperature of the aspiratory gas is lower than the body temperature, the absolute humidity of 44 mg/l may not be achieved even if the humidity is increased.
In the meantime, in the preferable HMEs:
an employed material and a manufacturing cost must be feasible in single-use;
a thermal resistance must be provided such that the temperature of an expiratory gas becomes approximately 23° C. at the side of anesthesia circuit or the respiratory circuit;
a thermal storage effect is required to regulate the temperature of the expiratory gas closer to the above temperature, 23° C., while avoiding increase in size, weight, dead cavity, flow resistance, and the like.
As an attempt of improving HMEs, a heat and moisture exchanging device provided with an auxiliary moisture and heat storage unit is proposed in Japanese Patent Application Laid-open Publication No. 2006-136461.
Further, as a modification of HMEs, in Japanese Patent Application Laid-open Publication No. 2000-225205, a mask that not only provides an improved humidifying function using a water-absorbing and water-retaining material but which also actively heats using a heat generator, thus adding heat and moisture, is proposed as a humidifying mask. In addition, a mask having a woven copper cloth for storing heat in an exhaled breath and adding the stored heat to an inhaled breath to warm the same in U.S. Pat. No. 5,706,802 and No. 6,196,221.
These heat and moisture exchanging devices do not have such functions as raising the temperature of the air to be inhaled and moisture absorption and release capabilities. In the existing heat and moisture exchanging devices, addition of a heater is required to achieve active heating function. Furthermore, in the above-mentioned masks, although heating of a gas to be inhaled is enabled, lack of moisture absorption and release capabilities may result in condense of water inside the mask.